1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member widely used for copying machines, printers, engraving systems, and the like apparatuses. The present invention also relates to an electrophotographic apparatus and a process cartridge employing the above electrophotographic photosensitive member.
2. Related Background Art
Conventionally, an electrophotographic photosensitive member is subjected directly to electric or mechanical action in the processes of electric charging such as corona charging and roller charging, development, image transfer, cleaning, and so forth, and is required to be resistant to the above actions.
Specifically, the electrophotographic photosensitive member should be resistant to abrasion and scratching by friction on the surface, and to electrical deterioration. In particular, in a charging system like a roller charging system utilizing electric discharge, the photosensitive member should be durable against high energy arc discharge.
Further, the surface of the electrophotographic photosensitive member should have higher cleanability in repeated toner development and toner cleaning without causing toner sticking to the surface.
To satisfy the above requirements for the photosensitive member surface, a surface protection layer mainly composed of a resin is provided. For example, Japanese Patent Application Laid-Open No. 57-30843 suggests a protection layer in which resistance is controlled by adding a particulate metal oxide as electroconductive particles.
Besides the protection layer, the incorporation of additives into the charge-transporting layer is studied to improve the properties of the photosensitive member surface. For example, silicone resins having a low surface energy are disclosed as below:
silicone oil (Japanese Patent Application Laid-Open No. 61-132954), polydimethylsiloxane, silicone resin powder (Japanese Patent Application Laid-Open No. 4-324454), crosslinked silicone resin, poly(carbonate-silicone) block copolymer, silicone-modified polyurethane, and silicone-modified polyester.
The typical polymers of a low surface energy includes fluoropolymers. The fluoropolymers below are useful as additives for the photosensitive layer: powdery polytetrafluoroethylene, and powdery fluorocarbons.
However, a surface protecting layer containing a metal oxide or the like, which has a higher hardness, tends to have a higher surface energy to result in lower cleanability and other shortcomings. A silicone type resin, which is advantageous as additives in lowering the surface energy, is less compatible with other polymers, so that it is liable to agglomerate in the photosensitive member to cause light scattering, or to bleed out of the surface to render unstable the properties of the photosensitive member. A fluoropolymer typified by polytetrafluoroethylene (PTFE) has a low surface energy, but is insoluble in solvents and less dispersible, producing a less smooth surface of the photosensitive member. Further, the fluoropolymer has a low refractive index, causing generally light scattering and deterioration of the latent image thereby.
High polymers like polycarbonate, polyacrylate esters, polyesters, and polytetrafluoroethylene are generally less resistant to arc discharge, and readily deteriorate by fission of the polymer main chain by electric discharge.